Question

100 ml water sample on titration with N/50 HCl required 12.4 ml for phenolphalein end point when methyl orange sample. was added to the same, pink colour developed. Describe the type and amount of alkalinity present in the water

Answer 1

Answer:

Titration of a sample by double indicator method using phenolphthalein and methyl orange can provide information on the components in the sample. When volume to the methyl orange endpoint (V

m

o

) is zero, only NaOH is present in the sample. When volume to the phenolphthalein endpoint (V

p

h

t

h

) is zero, only NaHCO

3

is present in the sample. If these volumes are equal, only Na

2

CO

3

is present in the sample. If V

p

h

t

h

< V

m

o

, NaHCO

3

and Na

2

CO

3

are both present in the sample. If V

p

h

t

h

> V

m

o

, NaOH and Na

2

CO

3

are both present in the sample.

Answer and Explanation: 1

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